The use of recycled cellulosic furnish to make towel and tissue products is increasingly desirable in view of the rising costs of virgin fibers, especially for facilities which use large volumes of absorbent products. Products made from recycle furnish tend to be relatively stiff, having relatively high tensiles and relatively low bulk leading to poor absorbency and properties. Moreover, these products tend to have relatively low wet/dry strength ratios. Various methods have been employed to increase the bulk and softness of products made from recycle furnish, including the use of softeners, debonders and the like as well as anfractuous fibers and/or new processing techniques; some of which require significant capital investment and cannot be readily adapted to existing production capacity such as conventional wet-press paper machines with Yankee dryers.
There is disclosed in U.S. Pat. No. 5,607,551 to Farrington, Jr. et al. throughdried tissues made without the use of a Yankee dryer. The typical Yankee functions of building machine direction and cross-machine direction stretch are replaced by a wet end rush transfer and the throughdrying fabric design, respectively. According to the '551 patent it is particularly advantageous to form the tissue with chemi-mechanically treated fibers in at least one layer. Resulting tissues are reported to have high bulk and low stiffness. Furnishes enumerated in connection with the Farrington, Jr. et al. process include virgin softwood, hardwood as well as secondary or recycle fibers. Col. 4, lines 28-31. In the '551 patent it is further taught to incorporate high-lignin content fibers such as groundwood, thermomechanical pulp, chemimechanical pulp, and bleached chemithermomechanical pulp. Generally these pulps have lignin contents of about 15 percent or greater, whereas chemical pulps (Kraft and sulfite) are low yield pulps have a lignin content of about 5 percent or less. The high-lignin fibers are subjected to a dispersing treatment in a disperser in order to introduce curl into the fibers. The temperature of the fiber suspension during dispersion can be about 140° F. or greater, preferably about 150° F. or greater and preferably about 210° F. or greater. The upper limit on the temperature is dictated by whether or not the apparatus is pressurized, since the aqueous fiber suspensions within an apparatus operating at atmosphere cannot be heated above the boiling point of water. Interestingly, it is believed that the degree of permanency of the curl is greatly impacted by the amount of lignin in the fibers being subjected to the dispersing process, with greater effects being attainable for fibers having higher lignin content. Col. 5, lines 43 and following. Lignin-rich, high coarseness, generally tubular fibers are further described in U.S. Pat. No. 6,254,725 of Lau et al. as well as U.S. Pat. No. 6,074,527 of Hsu et al. See also U.S. Pat. Nos. 6,287,422; 6,162,961; 5,932,068; 5,772,845; 5,656,132. The so-called uncreped, through-dried process of the '551 patent requires a relatively high capital investment and is expensive to operate inasmuch as thermal dewatering of the web is energy intensive and is sensitive to fiber composition.
Considerable commercial success has also been achieved in connection with U.S. Pat. No. 5,690,788 to Marinack et al. In accordance with the '788 patent there is provided biaxially undulatory single ply and multiply tissues, single ply and multiply towels, single ply and multiply napkins and other personal care and cleaning products as well as novel creping blades and novel processes for the manufacture for such paper products. Generally speaking, there is provided in accordance with the '788 patent a creping blade provided with an undulatory rake surface having trough-shape serrulations in the rake surface of the blade. The undulatory creping blade has a multiplicity of alternating serrulated sections of either uniform depth or a multiplicity of arrays of serrulations having non-uniform depth. The blade is operative to impart a biaxially undulatory structure to the creped web such that the product exhibits increased absorbency and softness with a variety of furnishes. Specifically disclosed are conventional furnishes such as softwood, hardwood, recycle, mechanical pulps, including thermo-mechanical and chemithermomechanical pulp, anfractuous fibers and combinations of these. Col. 20, line 41 and following. There is noted in example 20 of the '788 patent the improved properties obtained when using the undulatory blade in the manufacture of towels including up to 30 percent anfractuous fiber (HBA). The high bulk additive (HBA) is a commercially available softwood Kraft pulp sold by Weyerhauser Corporation that has been rendered anfractuous by physically and chemically treating the pulp such that the fibers have permanent kinks and curls imparted to them. Inclusion of the HBA fibers into the base sheet will serve to improve the sheet's bulk and absorbency. A significant advantage of the invention of the '788 patent over other advanced processing techniques is that it can be implemented with relatively low capital investment, and is compatible with processes employing mechanical dewatering.
The disclosure of the foregoing references incorporated herein by reference.
Despite many advances in the art, there is an ever present need for further improvements to products which incorporate cellulosic fiber such as recycle fiber, especially those improvements which do so on a cost-effective basis in terms of required capital and operating costs. It has been found in accordance with the present invention that there is a surprising synergy between the use of an undulatory creping blade and the incorporation of certain high yield fibers into the web as described hereinafter.